CODEOWNERS Migrate team cache to use slug instead of name

Confirm that uses of team are all based on slug (i.e. team as referred to in CODEOWNERS file) and not "Name" which can sometimes differ.

See example in REST API documentation for properies named `name` and `slug`: https://docs.github.com/en/rest/teams/teams?apiVersion=2026-03-10#get-a-team-by-name